This invention relates to electromagnetic scales having a permanent magnet system with an air gap and a coil arranged within the air gap through which flows a compensating current which varies as a function of the load being weighed.
It is a disadvantage of these known scales, that the heat generated by the compensating current flowing through the coil varies as a function of the load. Thus, the heat generated by the current through the coil will vary during sequential weighing of different loads. The heat generated by the current in the coil is of course proportional to the square of the current. The temperature within the scale thus changes continually, causing an instability in the zero point and possibly in the sensitivity of the scale. For example, for scales wherein the pan and the bending sections of the suspension are arranged in parallel, temperature changes result in changes in the mechanical tension and in differences in expansion, which in turn result in errors in the path along which the pan is to move. These effects are particularly annoying in very compact scales with high resolution. If these scales have a lever transmission, temperature differences at the lever can influence the sensitivity. These temperature change effects on the permanent magnet system can be reduced by means of correspondingly placed temperature sensors, but residual temperature errors caused by the heat inertia of the magnet system will remain.